Field of the Invention
The present invention relates to an apparatus for controlling the fuel injection timing of a fuel injection apparatus, and more particularly to a fuel injection timing control apparatus, in which the actual fuel injection timing of a fuel injection pump is directly or indirectly detected on the basis of a signal developed in response to the fuel pressure at the time of fuel supply, whereby the fuel injection timing is controlled by a feedback control system using the detected actual fuel injection timing.
In the prior art, there have been proposed various kinds of apparatuses for electronically controlling a fuel injection apparatus so as to obtain optimum fuel injection timing. In such conventional apparatuses the actual timing of fuel injection by a fuel injection pump is generally detected by a fuel injection timing detector and adjustment of the fuel injection timing is carried out by closed-loop control in such a way that the actual timing of fuel injection is made coincident with the optimum timing of injection determined in accordance with the operating condition of the engine at each instant. Consequently, when the fuel injection timing detector of the closed-loop control system malfunctions, it is impossible to continue appropriate control of the injection timing, with the result that the level of harmful components in the exhaust gas increases and fuel consumption rises.
To avoid these problems, there has been proposed a fuel injection timing control system in which the control mode is changed from feedback control based on the output signal from the fuel injection timing detector to open-loop control using no output from the fuel injection timing detector, if any malfunction of the fuel injection timing detector is detected (Japanese Patent Public Disclosure No. 110731/82). However, a variable inductance type position detector connected with the timer piston is used as the fuel injection timing detector in the control system disclosed in this publication, and malfunctioning of the fuel injection timing detector is determined on the basis of whether or not the output level of the position detector is within a predetermined range. Therefore, the disclosed system is not applicable to an apparatus in which the fuel injection timing is detected by the use of a detector that produces an electric signal showing the actual timing of the fuel injection in response to the fuel pressure at the time of fuel supply, such as a needle valve lift sensor.
More specifically, when the fuel injection timing of the fuel injection pump is directly or indirectly detected on the basis of a signal produced in response to the fuel pressure at the time of fuel supply by, for example, a needle valve lift sensor, since the timing detector stops producing the output signal when fuel injection falls to zero because, for example, the operator releases the accelerator pedal and uses the engine to brake the vehicle, it is impossible to distinguish the zero injection state from malfunctioning of the detector.